The cardiac sarcomere is composed of a highly organized set of protein assemblies giving rise to thick and thin filaments. Our studies will be focused towards comprehending the dynamic role these protein assemblies play in regulating the interactions among thick and thin filaments. Our approach will consist of isolating and purifying the various proteins and studying their physical-chemical properties. Efforts will be directed towards elucidating the role of the low molecular weight subunits, the "light chains" of myosin. One class of these light chains, the LC2, has been shown to be phosphorylated. Whether or not this phosphorylation results in changes of the molecular properties of cardiac myosin will be studied by enzymatic and hydrodynamic experiments as a function of calcium concentration. Experiments will also be designed to understand the reason for the existence of two active "heads" in cardiac myosin. The approach will involve actin-binding, ATPase and LC2 - recombination assays. We also plan to investigate the mechanisms involved in the switching on-off of cardiac muscle contraction. Attention will be centered on the effects of troponin phosphorylation on the Ca-regulatory function of the relaxing factor complex. In view of the positive inotropic effect of epinephrine and its important role in controlling cyclic AMP levels in the heart, it becomes important to relate these effects directly to phosphorylation of either troponin through cyclic AMP dependent protein kinases, or to LC2. These experiments will be performed in parallel with normal and myopathic hearts obtained from diabetic rats or myopathic hamsters; hypertrophied hearts from swimming rats and from hypertensive rats. Furthermore, comparative experiments with skeletal muscle proteins will complement this work and enhance our knowledge of the mechanisms operating in normal and myopathic heart. The dearth of experimental data animals makes it especially important to undertake such an investigation.